Structural state detection using quaternion-based three-channel joint transmissibility

This paper presented the use of quaternion-based three-channel joint transmissibility (QTJT) in structural state detection. During the detection process, the time-domain pure quaternion sequences were obtained based on the three dimensional spatial vibration signals from two different testing points. Then QTJTs of the object structure under different states were calculated by discrete quaternion Fourier transform (DQFT). Subsequently, modular vectors of the QTJTs were utilized to construct the state matrix of the object structure and the Karhunen-Loeve Transform (K-LT) was employed to calculate the state feature index vectors. Finally, Euclidean distance between state feature index vectors was obtained, which was considered as the state indicator. An actual experiment was performed on the test platform of ballastless track and the result with 100 percent correct identification was achieved. Combined with the experimental results, the advantages of QTJT comparing to transmissibility based on scalar signals were discussed. The QTJT can be used when the vibration composes from multiple dimensional synchronous vibrations. And more importantly, the QTJT is consistent with its theoretical value in spite of the installation orientation of the sensors

Structural state inspection using dual-tree quaternion wavelet transform

The dual-tree quaternion wavelet transform (QWT) was used in conjunction with quaternion-based three-channel joint transmissibility (QTJT) for state inspection. Multiple QTJTs from the same structural state were used to construct a state matrix, which was considered as a feature image. Then QWT coefficients of the feature image were calculated. It supported one magnitude and three phases, in particular, the low-frequency magnitude-phase was set as state feature index. Ultimately, the difference of the state feature indexes were utilized as the state indicator. This method reduced the influence on state inspection caused by measurement uncertainty of single testing sample, because it took overall consideration of multiple testing samples and described the similarity from multiple directions. The availability of suggested method was demonstrated by a real experiment, in which the state changing was realized by loosening fasteners and altering the longitudinal force of rail. This method was also compared with method based on Karhunen-Loeve Transform (K-LT) and artificial neural network (ANN). Experimental result indicated that the suggested method was integrated optimal, moreover, the resolution of the longitudinal force of rail was less than 10 MPa which was equivalent to temperature change of 1.75 °C for full-lock rail

Structural state detection using quaternion-based three-channel joint transmissibility

This paper presented the use of quaternion-based three-channel joint transmissibility (QTJT) in structural state detection. During the detection process, the time-domain pure quaternion sequences were obtained based on the three dimensional spatial vibration signals from two different testing points. Then QTJTs of the object structure under different states were calculated by discrete quaternion Fourier transform (DQFT). Subsequently, modular vectors of the QTJTs were utilized to construct the state matrix of the object structure and the Karhunen-Loeve Transform (K-LT) was employed to calculate the state feature index vectors. Finally, Euclidean distance between state feature index vectors was obtained, which was considered as the state indicator. An actual experiment was performed on the test platform of ballastless track and the result with 100 percent correct identification was achieved. Combined with the experimental results, the advantages of QTJT comparing to transmissibility based on scalar signals were discussed. The QTJT can be used when the vibration composes from multiple dimensional synchronous vibrations. And more importantly, the QTJT is consistent with its theoretical value in spite of the installation orientation of the sensors

Instrument for investigating the rail of a ballastless track under longitudinal temperature force

A longitudinal force loading instrument for rails was developed to simulate the longitudinal temperature force of the rail of a ballastless track under different rail temperatures. The instrument comprised the rail, an end-fixing device, a temperature force application device, and concrete foundation. This instrument could simulate the longitudinal stress distribution of the rail under different rail temperature changes and analyze the correlation between the natural frequencies of the rail and the longitudinal stress generated by temperature variation. The result of the longitudinal stress distribution exhibits good agreement with the simulation results. In addition, the result of the dynamic characteristics of the rail demonstrates good agreement with the former conclusions. This experimental instrument can be potentially developed into a powerful tool for researching the rail features of a ballastless track under different temperature forces

Online Condition Monitoring of a Rail Fastening System on High-Speed Railways Based on Wavelet Packet Analysis

The rail fastening system is an important part of a high-speed railway track. It is always critical to the operational safety and comfort of railway vehicles. Therefore, the condition detection of the rail fastening system, looseness or absence, is an important task in railway maintenance. However, the vision-based method cannot identify the severity of rail fastener looseness. In this paper, the condition of rail fastening system is monitored based on an automatic and remote-sensing measurement system. Meanwhile, wavelet packet analysis is used to analyze the acceleration signals, based on which two damage indices are developed to locate the damage position and evaluate the severity of rail fasteners looseness, respectively. To verify the effectiveness of the proposed method, an experiment is performed on a high-speed railway experimental platform. The experimental results show that the proposed method is effective to assess the condition of the rail fastening system. The monitoring system significantly reduces the inspection time and increases the efficiency of maintenance management

The Machine Vision Measurement Module of the Modularized Flexible Precision Assembly Station for Assembly of Micro- and Meso-Sized Parts

The machine vision measurement module is indispensable for the Modularized Flexible Precision Assembly Station (MFPAS), which is a fully automatic assembly system being developed at Dalian University of Technology (DUT). MFPAS consists of basic and additional modules, and are expected to be flexible, expandable, and re-configurable to adapt to a variety of parts with a large size range, requiring the machine vision measurement module to be able to achieve accurate measurement of position, as well as orientation of the parts with different size scale. An automatic zooming vision system was set up for evaluation and final integration in MFPAS. Pixel equivalent, principal point and orientation deviation of images were analyzed and experimentally studied using different magnifications of the lens. A new template with circular patterns of different diameters was designed for zoom-lens calibration. The experiments show that the measurement error caused by the variation of the pixel equivalent, principal point and orientation is estimated under 10 μm without online calibration. When high accuracy is required, online calibration can be employed during assembly. The evaluation results of the vision system with or without on-line calibration were given for a better trade-off between accuracy and efficiency during assembly

Key Technology of Data Registration for Large Aperture Aspheric Surface Measurement

Conference Name:5th International Symposium on Advanced Optical Manufacturing and Testing Technologies - Optical Test and Measurement Technology and Equipment. Conference Address: Dalian, PEOPLES R CHINA. Time:APR 26-29, 2010.Large measuring range and high resolution are always contradictories in practical measurement for large aperture aspheric surface. They must be met simultaneously in high precision measurement. Stitching method based on data registration is an effective way to resolve this contradiction. Aiming at the problem of rapid searching corresponding points, a key problem in offset sampling point set registration under rectangular coordinate system, a complete and effective approach is described in this paper. The original and destination point sets are registered roughly according to initial transformation and then projected to x-y plane. The intersection of two planar point sets' minimal bounding rectangle is solved to reduce the original points to be matched. The convex boundary of destination point set is solved and then principle of connected graphs is employed to judge whether one original point lies in destination point set. Strategy of space separating is employed to accelerate the neighboring points searching process. For each original point, its neighboring points belonging to a small area are solved. Subsequently, quadratic surface fitting is performed based on these neighboring points. Then method of Point-to-(Tangent) Plane is used to calculate its corresponding point. An emulation experiment is performed and experimental results are presented to show the feasibility of the proposed methods. It can realize rapid corresponding points searching effectively and meet the high precision registration under the situation of offset sampling

3-D Free-form Shape Measuring System Using Unconstrained Range Sensor

Fujian Provincial Natural Science Foundation for the Youth of China [2009J05136]; National Natural Science Foundation of China [50735003]Three-dimensional (3-D) free-form shape measurement, a challenging task pursued by computer vision, is mainly characterized with single view acquisition and multiple view registration. Most of the conventional scanning systems are less flexibility and difficult to realize engineering applications for employing sequential registration tactic. To develop portable scanning system and engineering registration method overcoming problems of error accumulation and propagation is the research direction. In this paper, one 3-D free-form shape measuring system using unconstrained range sensor is designed. A quasi-active stereo binocular visual sensor embedded within a scanning mechanism is used as the range sensor. Error compensation is performed by residual amendment according to camera calibration lattice. Artificial control points are designed and adhered on object and one camera is introduced to shot these control points from different positions and orientations. Then ray bundle adjustment (BA) method is used to calculate the space coordinates of all the control points, so as to set up a global control net work. Registration can be completed by mapping at least 3 control points observed by range sensor in single view acquisition into the global control network. In this system, no calibration for laser plane is required and the motion of range sensor is completely free. The overlapping of neighboring region is unessential for registration. Therefore, the working range of the system can be easily extended. The measuring precision mainly depends on the quality of global control network. The sequential distances of coding control points are observed by electronic theodolites and then compared with those obtained according to BA result. Experimental results show that relative distance error of control points is no more than 0.2%. The proposed measuring system is portable, provides good capacity for global error control, and contributes to the engineering application of 3-D free-form shape measurement